Bulk germanium has a direct band gap energy of roughly 0.8 eV, which is equivalent to about 1550 nm. Tensile strain lowers the band energy so that most wavelengths in the C-band can be absorbed at room temperature (roughly 20° C.). However, at lower temperatures, there is a shift of the band gap to high energies. Photons with low energy and long wavelength then are not able to be absorbed efficiently. This is an issue in products that can see a large temperature range during deployment. In particular, for products and devices that use germanium photodetectors, the responsivity would have to be specified to the worst case temperature. For some temperatures that are low enough, the product or device might not operate acceptably.
Also known in the prior art is Gebo, U.S. Pat. No. 5,130,920, issued Jul. 14, 1992, which is said to disclose a control system (method and apparatus) is adaptive on-line with changing process conditions, for example, the specific heat of a liquid used in a process. The system regulates a variable of a process (temperature of the liquid used in the process) and has a fast dynamic response to handle temperature transients while adapting to changing process conditions. The system uses feedforward and feedback control loops, which in the case of the process involving the temperature control of a liquid are respectively responsive to the temperature of the liquid before and after a control point. The system exercises adaptive control of the feedforward control function from the feedback loop. The system is preferably implemented with a digital computer. The fast dynamic response is enhanced by applying microwave energy from a microwave generator to heat the liquid at the control point with the feedforward and feedback control loops controlling the microwave generator.
Also known in the prior art is Wang et al., U.S. Pat. No. 8,274,021, issued Sep. 25, 2012, which is said to disclose an integrated temperature regulator that can be fabricated using conventional semiconductor processing technology. The integrated temperature regulator can include a reaction chamber, for example fabricated from PDMS, in which chemical or biochemical reactions of interest can be carried out. The temperature regular can also be used to regulate the temperature of some circuits, e.g. an effective-inductance-change based magnetic particle sensor, to achieve a stable operation performance, such as an improved sensitivity. The integrated temperature regulator includes as subcomponents a temperature sensing circuit that receives a thermal signal from the vicinity of the reaction chamber, a temperature reference circuit, and a temperature control circuit that controls a heater based at least in part on the difference between the sensed temperature and the reference temperature. The various subcomponents can be programmable.
There is a need for improvements in products and devices that employ germanium photodetectors and that may be operated under varying temperature conditions.